Method for the surveyance of an object space

ABSTRACT

In order to clearly reveal modifications, even small alterations occurring in a controlled object space (1), the thermal infrared radiation of the object space (1) is represented by means of an infrared objective (2) on two different infrared detectors (3, 4; 3&#39;, 4&#39;) and having each different spectral selectivity characteristics. Those two representations are serially scanned to form two sequences of electrical signals (5, 5&#39;). One of those signal sequences (5&#39;) is reproduced on a television monitor (7) directly in a predetermined color (8&#39;) and the reproduction of the other signal sequence (5) is delayed and is effected in another color (9&#39;).

The present invention relates to a method of monitoring a target space.

It is known that target spaces can be monitored by means of TV camerassensitive to infrared (IR) radiation. This produces an image that is inaccordance with the temperature differences and emission characteristicsof the target space. In general, an image of this kind displays littlecontrast and is only moderately sharp. Small changes in the target spaceunder surveillance are thus frequently missed by an observer.

It is an object of the present invention to provide a method which doesnot have these disadvantages, that is to say, in which even slightchanges in the space under surveillance will be made distinct.

According to the present invention there is provided a method ofmonitoring a target space, comprising projecting thermal infraredradiation of the target space by means of an infrared lens on to atleast one infrared sensitive detector, forming an electrical signalsequence by constant scanning, and passing this signal sequence in aspecific colour directly to a colour TV monitor and delayed and inanother colour to the same monitor as an image of the object.

In general, the objects in the target space differ from each other notonly by different temperatures, but also in the different emissioncoefficients of their materials. Thus, it is advantageous to project thetarget space on two detectors having spectral sensitivitycharacteristics that differ from each other, one of these detectorsbeing sensitive to IR radiation, and then repeatedly to scan the imagesso produced so as to form two signal sequences, and subsequently totransmit one of these signal sequences directly and in a specificcolour, the other delayed and in another colour, to a TV monitor.

In this connection, in order to render moving objects more distinct bymeans of a coloured outline, it is also advantageous if one transmits atleast one of these signal sequences both directly and in a specificcolour, as well as delayed, to a TV monitor.

It is advantageous to project the target space on at least one point,line or image-operating detector so that it is point, line or imagefiltered and to scan it in such a manner that point, line or imagesignal sequences result that correspond to two images having spectralsensitivity characteristics that differ from each other.

In order that the signal can be further processed by TV type systemsthat are commonly available it is desirable that TV type scanning beused, and at least one unit of line time.

In order to produce a stable image it is advantageous that a signal isdisplayed delayed by several units of line time.

In order that slow changes in the target space are rendered distinct itis further advantageous that a signal be displayed delayed by severalhalf-image or image times.

The present invention will be described in more detail by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a first embodiment for carryingout the method according to the present invention;

FIG. 2 is a schematic representation of a second embodiment for carryingout the method according to the present invention.

FIG. 3 is a schematic representation of a third embodiment for carryingout the method according to the present invention; and

FIGS. 4 to 9 represent various combinations of IR sensitive detectorwith the associated scanning systems and possible filtering and picturesectioning systems.

As can be seen from FIG. 1, the target space 1 is projected onto adisplay screen 3 by means of an IR lens 2. The display screen 3 isscanned repeatedly by line and by image in the manner of a TV, by meansof a scanning system 4 so as to produce a signal sequence 5. The signalsequence 5 corresponds to a conversion of the geometrical imageinformation into time information.

The time information 5 is transmitted, on the one hand, directly, and onthe other hand through a delay circuit 6 to a two-colour TV monitor 7.

In this regard, a stable image 1 is reproduced in that the signalsequence 5 that is transmitted directly is reproduced as an image thatoverlaps the image that results from the signal sequence that istransmitted through the delay circuit 6. In principle, however, the twosignal sequences are reproduced by two different signal sequences, andfor this to the mixing of the two colour images for a stable image.

Conditions change as soon as a part of the image moves, since then themoving and the stationary parts display different colours since on theone hand the signal sequence transmitted directly, and on the other thesignal sequence that is transmitted through the delay circuit 6 to themonitor 7 no longer overlap and this results in differently colouredimages 8 and 9.

In FIGS. 2 and 3, the same identification numbers are used to identifythe same components as in FIG. 1.

However, a spectral image division 10 is also provided for, and theeffect of this is that the bundle of rays that produce the image 3 issplit so that the images 3 and 3' correspond to different spectralranges of the object radiation.

The images 3 and 3' corresponding to the two different spectral rangesare converted into two signal sequences 5 and 5' by the scanning systems4 and 4'; signal sequence 5 is passed to the colour monitor 7 throughthe delay circuit 6 and signal sequence 5' is passed to the colourmonitor 7 directly. The image 8' of a stationary object is changed bythe splitting of the spectral range by means of the spectral imagesectioning, in that now spectrally different radiating objects will bereproduced in different colours even if not moving. In addition, amoving object will be rendered distinct by a colour outline or by beingdifferently coloured 9'.

In FIG. 3, unlike FIG. 2, the signal sequence 5 is not only delayed, butalso transmitted directly and the signal sequences 5, 5' and 5a arereproduced as three different colours on the colour monitor 7. For thisreason, the image appears without movement in colours that consist oftwo primary colours, each according to the spectral emissioncharacteristics of the target space, and it appears in colours thatconsist of three primary colours as soon as there is any movement in thetarget space.

FIG. 4 shows the use of a detector system 31 that reproduces a singleimage point. Image scanning is by means of a mirror system 41, and iscarried out vertically and horizontally.

FIG. 5 shows a detector system 32 that consists of a plurality ofindividual elements, each having a corresponding switch 45, thesecorresponding for example to the image points per line. For this reasonthe scanning system 42 only operates vertically.

FIG. 6 shows a mosaic arrangement 33 of the detector elements and allthe scanning is by electronic step switching.

FIG. 7 shows a large-area detector element 34, for example, a pyrikon,scanning being by means of an electron beam. A rotating filter disc 104serves as an image divider.

FIG. 8 shows an arrangement corresponding to FIG. 7, in which, however,the image divider has been replaced by a strip filter 105.

FIG. 9 shows an arrangement similarly to FIG. 7, in which, however, theimage divider consists of a prism system 106 as described, for example,in Swiss Patent, No. 10615/79-8.

I claim:
 1. A method of monitoring a target space, characterised byprojecting thermal infrared radiation of the target space by means of aninfrared lens on to at least one infrared sensitive detector, forming anelectrical signal sequence by constant scanning and passing this signalsequence in a specific colour directly to a colour TV and delayed and inanother colour to the same monitor as an image of the object.
 2. Amethod as in claim 1, wherein the target space is projected on to twodifferent detectors, which have different sensitivity characteristics,of which at least one is infrared sensitive, these images being scannedrepeatedly so as to form two sequences of electrical signals, thesesequences then being displayed on the TV monitor, one sequence beingtransmitted directly in one specific colour, the other being delayed andtransmitted in another colour.
 3. A method according to claim 2,characterised by that at least one of these signal sequences istransmitted to the TV monitor, both direct and in a specific colour aswell as delayed.
 4. A method according to claim 1, characterised by thatthe target space is projected on a point, line or image operatinginfrared detector so as to be displayed point, line or image filteredand so scanned that point, line or image signal sequences result, thesecorresponding to at least two images that have spectral sensitivitycharacteristics that differ from each other.
 5. A method according toclaim 1, characterized in that TV type scanning is used, and that atleast one signal sequence is reproduced delayed by at least one unit ofline time.
 6. A method according to claim 1, characterized in that asignal is reproduced delayed by several units of line time.
 7. A methodaccording to claim 1, characterised by that a signal is reproduceddelayed by several units of half-picture or picture time.
 8. A method asin claim 1 wherein: the scanning during said step of forming is a linescanning; in the monitor the image is formed by line scanning; and thedelay imparted to the signal sequence is equal to an integral multipleof one line scanning period.